Biomechanical testing of titanium self-tapping versus pretapped lag screw fixation of spiral metacarpal fractures

Biomechanical tests of torsional loading and cantilevered bending were used to study the effects of varying screw size and design of five different titanium miniscrews and microscrews in a metacarpal spiral oblique fracture model. Sixty-six fresh frozen human cadaveric metacarpal bones were subjected to torsional loading until failure, producing a spiral oblique fracture. The randomized fractured metacarpal bones were then repaired utilizing two 1.2- mm, 1.7-mm, or 2.3-mm self-tapping Leibinger lag screws; and 1.5-mm or 2.0- mm pretapped Synthes lag screws. Following repair, the specimens were then subjected to cantilevered bending or torsional loading. Failure torque and bonding loads were then used to calculate failure stresses at the midshaft for torsional loading or at the proximal screw for cantilevered bending. Analysis of variance statistical analysis revealed that within the cortical thickness of bone studied, no significant difference in shear stress or axial stress was observed with increasing screw diameter and screw design.